Granular ammonium perchlorate propellant

ABSTRACT

Granular ammonium perchlorate having a particle size of -40 to 50 mesh is packed to a bulk density of from about 1.0 to 1.5 g/cc in a rocket motor casing restricted to maintain a chamber pressure in the range of from about 100 to about 2,000 psia and is used as the sole source of propellant gases for propelling a rocket. A flame similarly provided may be used for other pyrotechnic applications.

[is] 3,656,432 1 Apr. 18, 1972 United States Patent Hackman, Ill

X R n 1 w m m S m F u n B m J 6 r m z m m It a m n m A L ML E IP N0 OR PE n RR 0 L H C MR E GP M H Attorney-Emil W. Milan [72] Inventor: ElmerEllsworth l-lackman, III, Hockessin,

Del.

[73] Assignee: ABSTRACT Granular ammonium perchlorate having a particlesize f Thiokol Chemical Corporation, Bristol, Pa.

to mesh is packed to a bulk density of from about L0 to 1.5 g/cc in arocket motor casing restricted to maintain a chamber pressure in therange of from about to about 2,000 psia and is used as the sole sourceof propellant gases for propelling a rocket. A flame similarly providedmay be used for other pyrotechnic applications.

44 6 @0057 8 9 4 4 1 o 1 1 3 0 H7 0 0 MNQ 25 49 7 U A 6 I 0 4 4 J 9 n mu9 m wM 2 9 u. 6 m m 9 u u I. H mm u. J m WW 7 u u" a 2 m Ch M 8 mm 1 N"I U 9 M H S l .f o a w Cd v -II N PS Mk F AU IF i .111 .1] 2 2 00 2 255-3 [56] References Cited UNITED STATES PATENTS 3,056,701 10/1962Fritzlen..................................l02/99 scl'flmmmmwgmPATENTEDAPR 18 I972 3. 656.432

Elmer E llsworfl) HackmanJU I N VENTOR.

ATTORNEY GRANULAR AMMONIUM PERCI'ILORATE PROPELLANT BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates to rocketmotors and particularly to a solid propellant system used to operate arocket motor.

2. Description of the Prior Art Solid propellants for operating rocketmotors are usually fcomposite" types, such as rigid composites,elastomeric composites, or thermoplastic composites, such as thosedescribed, for example, in The Chemistry of Propellants, Penner andDucarme, Pergamon Press, New York (I960), pages 285-302, chapterentitled Methods of Burning Rate Control in Solid Propellants byG.l-l.S. Young. Such composites generally are composed of an oxidizer,which usually is ammonium nitrate or a perchlorate, e.g. ammoniumperchlorate, and a fuel, which may be an organic compound, e.g. pitch,styrene polymers, or a polysulfide rubber, and/or a metal fuel, forexample, aluminum powder.

From the work of G.K. Adams, discussed at pages 297 298, supra. it isknown also to burn ammonium perchlorate pellets under nitrogen pressureabove 1,000 psi, or at a lower pressure, if a sufficiently large surfaceis exposed, or if a catalyst is used. However, as further discussed byG.H.S. Young at page 298, supra, the information so far available hasnot enabled one to make predictions about the burning rate of ammoniumperchlorate, which is found to be the fastest of the group tested,consisting of ammonium nitrate, double base and ammonium perchlorate.

Also, in US. Pat. No. 3,056,701 is taught a composite solid fuel packageuseful in rocket gas generating systems, and employing a mixture of agranular solid perchlorate oxidant and aluminum or magnesium powderloosely disposed essentially between layers of flat aluminum ormagnesium foil which serve both as a fuel and as a safeguard againstpenetration of hot gases throughout the mass thereby to reduce the riskof explosion.

Each of the above systems essentially comprises an organic or metal fuelin combination with the oxidizer, usually in at least a stoichiometricratio. None teaches use of ammonium perchlorate alone as aself-sustaining sole, gas generating means, as does the presentinvention.

SUMMARY OF THE INVENTION The present invention provides a means foroperating a rocket motor or other pyrotechnic device, e.g. a metalcutting torch, with ammonium perchlorate as the sole source ofpropellant gases or flame. It has now been discovered that by packinggranular ammonium perchlorate essentially having a particle size of fromabout 40 to about +50 mesh (all retained on U.S. Standard sieve size 40mesh, all passes sieve size 50 mesh) to a density of from about 1.0 toabout 1.5 g/cc, in a rocket motor casing fitted with an exhaust nozzlethrottled or otherwise restricted, to maintain chamber pressure belowabout 2,000 psia, the ammonium perchlorate can be ignited and will burnwithout exploding while generating propellant gases in sufficient volumeto propel] the rocket in which it is contained. Contrary to formerteachings, it has been found that compression of the ammoniumperchlorate into a voidfree mass is not necessary to achieve burning ofthe ammonium perchlorate without explosion. It has also been found thatpresence of a supplemental organic or inorganic fuel ingredient is notnecessary to propagate the flame after ignition.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates schematically across-sectional, partially broken away, expanded view of the componentsof a rocket motor driven munition provided with propellant according tothe invention.

More specifically, a rocket motor casing 1, made of high strengthphenolic resin or other inert casing material and having a single openend 7, is packed first with a layer of lightweight, non-combustiblewedding 2, which is used as a spacing material to vary the length of thepropellant charge and, accordingly, its burning time. The casing I isthen packed with propellant 3 which consists of 40 to +50 mesh granularammonium perchlorate as the sole gas generating charge and which isdensified by means of a vibrator to a density of about 1.0 to 1.5 g/cc.An igniter assembly 4, provided with electrical ignition means 5, isinserted into the propellant mass through an opening 6 provided near theopen end 7. The open end 7 is then sealed with a sealing diaphragm 8which is made of a rupturable plastic or elastomeric composition. Anozzle assembly 9 is attached to the open end 7 of the casing I by meansof threads 10 which engage threads ll of the casing. An ogiveshapedpayload head 12, provided with a payload I3, is attached to the closedend 14 of the casing I by means of threads 15 which engage threads 16 onthe head 12. The casing 1 is provided with stabilizer fins 17 in theusual way. The nozzle assembly 9 is coated internally with carbon throatlining 18 and has its restricted outlet 19 sized to maintain thepressure within the casing 1 below a desired design pressure in therange from about to about 2,000 psia during combustion of the propellant3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is practiced byusing, as substantially the sole gas producing component in thepropellant 3, ammonium perchlorate granules or crystals which are of theusual high grade chemical specifications used in rocket propellantcompositions. However, the particle sizes of the granules or crystals iscontrolled by screening out particles finer than 40 mesh U.S. Standardsieve size and excluding particles over 50 mesh in size. The particlesthus have a size of from about 300 to about 400 microns measured alongtheir narrow axes. The granules may be in any form, e.g. crystals,spheres, or ground particles. lrregularly shaped particles are preferredfor their better packability. The particles are poured, or otherwisecharged, into the casing l and are compacted to a density of from about1.0 to about 1.5 g/cc, for example, by placing the casing l in avertical position with the closed end 14 resting on the surface of avibrating table. The rocket casing l is then prepared for assembly andassembled substantially as described above and illustrated in thedrawing.

A series of burning tests were carried out in a strandburner in order todetermine the burning rates of high purity ammonium perchlorate atvarious pressures. The strandburner procedure used was patterned afterthat of B.L. Crawford et a1. Anal. Chem, 19, 630 (I947), described anddiscussed at pages 288289 of The Chemistry of Propellanr, supra. Ingeneral, strandbumer tubes having an inner diameter of 4 mm were used.Burning rates were determined at pressures of [,520, 1,015, 615, 315 andpsia, using -40 to +50 mesh powder packed to a bulk density of H0 g/cc 5percent. The test data and results are shown in the table.

TABLE Example No. of Test Burning Rate No. Samples Pressure psiainches/sec.

l 8 I520 llllfllfil 2 9 l0l5 9.49:.31 3 9 615 6.671216% 4 9 M5 4.522254;5 8 I05 2.111303% From the data in the examples shown in the table, theformula for rate of burning of the ammonium perchlorate was calculatedin accordance with the usual formula R,=kp", where R, is the rate ofburning in inches per second,

k is a constant for the given propellant,

p is the combustion pressure in psia, and

n is the pressure exponent.

The burning rate may be modified by combining the ammonium perchloratewith small amounts of burning rate catalysts such as manganese compoundsto increase the buming rate, or with finely divided refractory materialsin a manner and in amounts known to be used in the burning of 5 ammoniumperchlorate compositions in the presence of a fuel, such as anelastomer.

In addition to the advantages and benefits described above, the use ofammonium perchlorate as the sole gas generating component in the rocketcasing has the advantage that the rocket assembly has a greaterresistance to shock of impact than does the usual composite type ofammonium perchloratecontaining propellant. Whereas the impactsensitivites of the latter composite types run about 20 inch pounds,that of the ammonium perchlorate sole propellant of the invention runsover 100 inch pounds.

Upon ignition, the compacted ammonium perchlorate burns to producepropellant gases substantially in accordance with the combustionequation of B. H. Newman, given at page 33 of ACS Monograph No. 146,Perchlorares, Reinhold Publishing Company, I960):

While it is not known definitely why the ammonium perchlorate particlesof -40 to +50 mesh size, when packed to a density of L to L g/cc, burnsmoothly rather than explode, at a burning pressure in the pressurerange of from about 100 to about 2,000 psia, it is theorized that theclosely packed particles of ammonium perchlorate form a substantiallysolid barrier to gases which prevents the hot combustion gases fromreadily entering into the randomly occurring spaces between theparticles without loss of sufficient heat to reduce the temperature ofthe particles below an explosive temperature at a given pressure.Whatever the reason, it has been found that the particulate ammoniumperchlorate burns smoothly, forming a self-sustaining flame to providethe gases needed to propel] a rocket motor designed and made inaccordance with known rocket design and manufacturing principles.

The self-sustained burning of ammonium perchlorate particles accordingto the invention may also be used to provide a flame source for metalcutting. [n such use, the oxygen and chlorine gases present in theproducts of combustion provide an added benefit in that they combineexothermically with the metal being worked, e.g. iron, to form an evenhotter cutting flame. The invention thus provides a flame source whichis particularly advantageous in performing rescue or demolitionoperations in remote locations where cylinder gases cannot be brought tothe scene. A torch-type container for low pressure (e.g. about lOO 200psia) operation may readily be designed and built to carry out such anoperation in combination with the present invention.

Although certain specific embodiments have been shown and describedherein, it is to be understood that they are illustrative only and arenot to be construed as limiting on the scope and spirit of theinvention.

Iclaim:

l. A pyrotechnic device having an open-ended combustion chamber having arestricted outlet and consisting essentially of, as substantially thesole gas or flame generating component contained in the device, ammoniumperchlorate particles having a particle size in the range of from about40 to about +50 U.S. Standard sieve size compacted in the combustionchamber to a density in the range from about 1.0 to about 1.5 g/cc, saidoutlet being restricted to maintain the pressure of the products ofcombustion in the combustion chamber in the range of from about lOO toabout 2,000 psia during combustion of the ammonium perchlorate.

2. A pyrotechnic device according to claim I wherein the device is arocket motor and the products of combustion are used to drive the motor.

3. A pyrotechnic device according to claim 1 wherein the device is acutting torch and the flame of combustion is used as a cutting flame.

2. A pyrotechnic device according to claim 1 wherein the device is arocket motor and the products of combustion are used to drive the motor.3. A pyrotechnic device according to claim 1 wherein the device is acutting torch and the flame of combustion is used as a cutting flame.